Renaming README.txt to index.rst solved the double entries issue but it also removed to sphinx gallery thumbnails. Do we need the thumbnails?

OLD:

NEW:

I would prefer the thumbnails over the headings, but that is a mild preference. If getting that is hard this is 👍

Ha ha. OK, we are whack-a-moling sphinx/sphinx-gallery weirdness here.

#26141 added the manual TOC so that the cards in https://matplotlib.org/devdocs/users/explain/index.html would have subsections (see the Color card). If you remove the manual TOC, then the sphinx-gallery TOC is hidden and doesn't show up as a subsection. However, it appears that the left bar is somehow able to parse both the hidden and the visible TOC.

There seem to be a few ways to fix this

0. make the cards ourselves, and don't let sphinx gallery make the index.rst (basically this PR).
1. sphinx gallery optionally allows the TOC they generate to be visible instead of "hidden"
2. pydata sphinx theme could respect "hidden" (however I expect they don't respect "hidden" because folks want sphinx gallery to work).
3. Somehow make TOC entries for user/explain/index include hidden index.

Ah, 3 is probably the best bet

.. toctree::
   :includehidden:

So the todo here is 1) remove the manual TOC entries in #26141 and fix users/explain/index entries to have :include hidden:. @StefRe happy for you to do this, or I'm happy to do it.

@jklymak I would be grateful if you could finish this. I tried several things but I admit didn't fully understand what I'm doing actually, so it would be great if you could make this work so maybe I can learn how things work here.
Maybe it's easier to close this PR and you make a new one - I'm happy with any solution.

Sure, if OK it'll be easier for me to just open a new PR. Thanks for noticing the issue!